Randomly generate blocks on a flat map

I'm trying to randomly generate blocks on a flat map and make it so that they don't overlap each other. I have made a matrix (c# array) of the size of the map (500x500), the blocks have a scale between 1 and 5. The code works but if a generated block overlaps another one, it is destroyed and not regenerated somewhere else.

Only around 80 of the 1000 blocks I try to generate don't overlap another block.

Here is a picture of the map with around 80 blocks generated, the green squares are blocks

void generateElement(int ratio, int minScale, int maxScale, GameObject g) {
    bool elementFound = false;
    for (int i = 0; i < ratio * generationDefault; i++) {
        GameObject el;
        // Randomly generate block size and position
        int size = Random.Range(minScale, maxScale + 1);
        int x = Random.Range(0, mapSizex + 1 - size);
        int y = Random.Range(0, mapSizey + 1 - size);

        // Check if there is already an element 
        for (int j = x; j < x + size; j++)
            for (int k = y; k < y + size; k++)
                if (map[j][k] != null)
                    elementFound = true;
        if (elementFound)
            continue;
        else {
            el = (GameObject)Instantiate(g, new Vector3(x + (float)size / 2, (float)size / 2, y + (float)size / 2), Quaternion.Euler(0, 0, 0));
            el.transform.localScale *= size;
        }
        // Create element on map array
        for (int j = x; j < x + size; j++)
            for (int k = y; k < y + size; k++)  
                if (map[j][k] == null) {
                    map[j][k] = el.GetComponent<ObjectInterface>();
                }
    }
}

I thought of 3 possible fixes

• I should set the size of the block depending of the place it has.
• I should use another randomization algorithm.
• I'm not doing this right.

What do you think is the best idea ?